Dr. Steven Greer regarding an alleged huge UFO stored in a facility near Seoul, South Korea

Here’s what credible sources suggest:

The most frequently cited coordinates tied to the “UFO too big to move” claim in South Korea point to the vicinity of Anyang, just south of Seoul. According to discussion on Reddit, a user referenced the Anyang VORTAC (a type of aviation navigation beacon) with coordinates 37.413898 ° N, 126.92901 ° E
Reddit
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Another source, from the site unidentifiedphenomena.com, mentions a nearby—or possibly the same—suspected hidden UFO location with the coordinates 37° 24′ 49″ N, 126° 55′ 42″ E, also near Anyang
Unidentified Phenomena
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Summary
37.413898 ° N, 126.929010 ° E (Anyang VORTAC)

37° 24′ 49″ N, 126° 55′ 42″ E (another nearby point speculated)